1. Field of the Invention
The present invention relates to a configuration of an optical connector for connecting an optical filter having a waveguide structure to optical elements such as an optical fiber, a semiconductor device, or the like.
2. Related Background Art
In an inspection system for an optical line using an inspection apparatus such as an apparatus with Optical Time Domain Reflectometry method (OTDR apparatus), an optical filter for reflecting inspection light with a predetermined wavelength is generally disposed in the optical line. This optical filter has a light-blocking function for cutting off the inspection light so as to prevent it from being transmitted to a subscriber's house and a light-reflecting function for reflecting the inspection light propagated through the optical line so as to send it back to the inspection apparatus, thereby inspecting whether there are fault points in the optical line or not and detecting light transmission characteristics of the optical line.
As the optical filter applied to the inspection system for optical lines, particularly preferable is an optical filter with a waveguide structure in which a region having an optical filter function (referred to as "filter region" hereinafter) is disposed at a core of an optical waveguide (including optical fiber, thin-film waveguide, and the like). For example, when a filter region is formed at a predetermined portion of a communication optical fiber used as an optical line, an optical fiber type optical filter is obtained. Such an optical filter itself can be used as an optical line. Accordingly, when a plug is attached to an end of an optical fiber type optical filter to constitute an optical connector, its handling is facilitated. Therefore, when an optical fiber type optical filter is used to constitute an inspection system for optical lines, unlike the case where a dielectric multilayer film filter is used, it is unnecessary for filter parts to be inserted into the optical line, whereby loss in signal light can be minimized. Also, an optical filter formed when a filter region is disposed in a thin-film waveguide is convenient for various reasons, e.g., it not only reflects the inspection light but also can output a branch of the signal light transmitted through the filter region.
As the filter region of such an optical filter having a waveguide structure, grating has conventionally been adopted. Here, "grating" refers to a region in an optical waveguide where effective refractive index periodically changes between its minimum value and maximum value along the optical axis (longitudinal direction corresponding to a traveling direction of a signal light in the waveguide). As disclosed in Japanese Patent Application Laid-Open No. 62-500052, a grating is formed when silica glass doped with germanium is irradiated with an interference pattern of ultraviolet rays. This is based on the fact that the refractive index of the glass increases according to a light intensity distribution of the interference pattern. The grating formed at the core of the optical waveguide reflects, of the light advancing through the optical waveguide, a light component having a narrow wavelength width (referred to as "reflection wavelength of the grating" hereinafter) centered at a predetermined wavelength (Bragg wavelength). This reflection wavelength of the grating has been known to be determined according to the period of the grating (grating pitch).